For instance, someone was cleaning out their 
gallery, and I saw a cel that would usually go 
for about $35-50, fair market value. I emailed an 
offer towards the higher end of that... and it 
turned out they wanted at least $110 for it, 
which is what they said they had paid the dealer 
for it.

So what should I do? Should I laugh at them and 
tell them the dealer had taken advantage of them 
and no one in their right mind would have paid 
$110 for it? Should I try and haggle them down, 
telling them that they're not likely to get any 
offers anywhere near that, so go ahead and sell 
to me? Should I show them the link to the YJ 
auction of a same-sequence cel that ended for 
4000 yen? Should I show them the cel I have 
that's better-than-theirs and tell them I only 
paid $30 for it?

Nope. If the person wants to sell a cel at a 
certain price, that's their right. But I don't 
have any obligation to tell them why I don't want 
to accept their counter-offer if it's not to my 
liking. If they're sincerely curious about my 
feelings, perhaps... but I doubt that any of the 
suggestions above would be well-received. ^_^ 
Obviously, the cel is worth more to them than it 
is to me, so I'll let them keep it until they 
find a better buyer with deeper pockets. :o)

Now, if I had made you an offer on your cel, and 
you had accepted it, you would have a genuine 
right to be peeved if I didn't follow through. 
^_^ But until both parties agree, there's no 
obligation on either side.

-Cres